Structured lighting detection of vehicle occupant type and position

ABSTRACT

An apparatus ( 12 ) for determining the location of a vehicle occupant ( 20 ) in a vehicle interior includes a light source ( 40 ) for projecting at least one structured light beam ( 42 ) onto an area of interest ( 44 ) to form a light pattern on the area of interest. A beam divergence control device ( 50 ) alters the apparent location of the light source ( 40 ) with respect to the area of interest ( 44 ). An imager ( 60 ) detects the light reflected from the area of interest ( 44 ). A characteristic of the reflected light is measured, and the distance between the imager ( 60 ) and the area of interest ( 44 ) is measured, based on the measured characteristic of the reflected light.

TECHNICAL FIELD

[0001] The present invention is directed to an occupant sensing systemand an associated method, and is particularly directed to occupantsensing using an image sensor to sense an occupant.

BACKGROUND OF THE INVENTION

[0002] Occupant protection systems are well known in the art and areemployed in vehicles to help protect vehicle occupants during a vehiclecrash event. Most occupant protection systems include one or moreactuatable components, such as an air bag, a seat belt pretensioner, aside curtain, etc. During a crash event, these components may beactuated to help protect the vehicle occupant.

[0003] Deployment or actuation of the actuatable component is usuallydependent upon numerous criteria, such as crash conditions and/oroccupant characteristics. A crash condition may be indicated by a crashmetric, such as crash acceleration, crash velocity, crash displacement,etc. For example, if a crash metric, such as crash acceleration, isgreater than a predetermined threshold crash acceleration value, thenthis may be regarded as an indication that the crash event is adeployment crash event (e.g. a crash event having a magnitude and/orduration great enough to warrant actuation of the actuatable protectioncomponent).

[0004] Relevant occupant characteristics may include presence, position,and weight of the occupant. With reference to an air bag, for example,deploying the air bag is wasteful if an occupant is not present. Also,depending on the size and position of an occupant that is present,deploying the airbag may not enhance protection of the occupant; thus,it may be desirable to suppress actuation. Alternatively, depending onthe size and position of an occupant who is present, it may be desirableto limit the pressure of the inflation fluid in the inflated air bag.

[0005] Several different arrangements and methodologies have beendeveloped to sense these occupant characteristics. For example, imagingtechnologies have been utilized to acquire an image of the interior of avehicle to determine the presence and/or position of an occupant.

[0006] U.S. Pat. No. 6,005,958 shows an occupant type and positiondetection system that uses an infrared camera to generate image data ofthe front seating area of a vehicle. The data are used to track occupanttype and position relative to a fixed structure such as the vehicleinstrument panel, to optimize the controlling of deployment of anoccupant safety device, such as an air bag.

[0007] U.S. Pat. No. 5,531,472 discloses an image sensor that is used toobtain image data which is representative of an occupant on a vehicleseat. The image data is compared to stored image data to obtain theoccupant's size and position within the vehicle.

[0008] U.S. Pat. No. 5,528,698 discloses an image sensor that acquires arepresentation of the passenger seat area within a vehicle. Objectswithin the field of view of the sensor are discriminated to determinewhether a rear facing child seat is located in the passenger seat.

[0009] In some cases, structured lighting (as opposed to diffuselighting) is used to create a 3D visual image of an object. Structuredlighting alone does not, however, provide sufficient coverage to support2D occupant recognition techniques. In addition, the source of astructured light must be located at a position and perspective thatdiffers sufficiently from that of the camera to allow recognition of thedistortions created by overlaying the structured lighting on an objectthat has 3D structure. This results in the added cost of extended ordual packaging to accommodate the spaced locations of the camera andlight source.

SUMMARY OF THE INVENTION

[0010] In one aspect, the present invention is an apparatus fordetermining the location of a vehicle occupant in a vehicle interior.The apparatus comprises a light source for projecting at least onestructured light beam onto an area of interest in the vehicle interiorto form a light pattern on the area of interest. A beam divergencecontrol device alters the apparent location of the light source withrespect to the area of interest. An imager detects the light reflectedfrom the area of interest. A characteristic of the reflected light ismeasured, and the distance between the imager and the area of interestis measured, based on the measured characteristic of the reflectedlight.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The foregoing and other features of the invention will becomeapparent to one skilled in the art to which the invention relates uponconsideration of the following description of the invention withreference to the accompanying drawings, in which:

[0012]FIG. 1 is a schematic illustration of a vehicle that includes anoccupant location system in accordance with a first embodiment of theinvention;

[0013]FIG. 2 is an illustration of a determination of the location of anobject by the system of FIG. 1;

[0014]FIG. 3 is a schematic view of a portion of a light patternprojection by an occupant location system in accordance with a secondembodiment of the invention;

[0015]FIGS. 4 and 5 are views similar to FIG. 1 of an occupant locationsystem in accordance with a third embodiment of the invention; and

[0016]FIGS. 6 and 7 are views similar to FIG. 1 of an occupant locationsystem in accordance with a fourth embodiment of the invention.

DESCRIPTION OF THE INVENTION

[0017]FIG. 1 illustrates portions of a vehicle 10 that includes anoccupant protection system 12. The system 12 includes an occupantlocation system 14 in accordance with the present invention. The vehicle10 also includes an instrument panel 16 and an occupant seat 18, onwhich is shown seated a vehicle occupant 20.

[0018] The illustrated occupant protection system 12 includes an air bagmodule 22. An air bag 24 of the module 22 is operatively stored in afolded condition within a housing 26 of the module. The housing 26 ismounted on the instrument panel 16 of the vehicle 10.

[0019] The module 22 includes a source 28 of inflation fluid (e.g., gas)to inflate the air bag to a deployed state (not shown). The inflationfluid source, or inflator, 28 may include pyrotechnic material that isignited by a squib. Combustion of the pyrotechnic material generates gas(e.g., nitrogen gas). In an alternative embodiment, the inflation fluidsource 28 may include a pressurized container of gas. The configurationof the occupant protection system 12 is not a limitation on the presentinvention, and the illustrated embodiment provides only an exemplaryenvironment for the present invention.

[0020] A crash sensor 32 is included within the occupant protectionsystem 12 to sense a vehicle crash event and output a signal indicativethereof. A controller 34 receives the signal from the crash sensor 32.The controller 34 controls actuation of the air bag module 22 based onthe output signal from the crash sensor, among other inputs. Thecontroller 34 is typically a microcomputer or microprocessor.Alternatively, the controller 34 may be provided by one or more digitaland/or analog circuits. Also, the controller 34 may be provided withinan application specific integrated circuit.

[0021] The controller 34 is operative to control the rate and degree ofair bag inflation, so that the deployment of the air bag 24 isadjustable. In the illustrated example, the deployment of the air bag isadjustable by use of a vent device 38 that is connected to the housing26 or the air bag 24. The vent device 38 may take any one of a varietyof forms, such as an electrically controlled regulator or valve thatresponds to a control signal.

[0022] Another function of the controller 34 is to make determinationsregarding the presence and/or position of an occupant. Thedeterminations of the presence and/or position of an occupant are basedupon sensory information and are used to help control theactuation/adjustment of the air bag 24. Thus, the controller 34 is partof the occupant location system 14.

[0023] Another part of the occupant location system 14, and part of thestructure for obtaining sensory information regarding the presenceand/or position of the occupant, is an illuminating element in the formof a structured light source 40. The structured light source 40 islocated within the interior of the vehicle 10. The structured lightsource 40 is operatively connected to the controller 34 and selectivelyilluminates the interior of the vehicle 10 with structured light asdescribed below in response to a control signal provided by thecontroller 34. By selectively illuminates, it is meant that thestructured light source 40 illuminates the interior of the vehicle 10only when it is turned on or activated by the controller 34. Thestructured light source does not illuminate the interior of the vehicle10 when it is not turned on or not activated by the controller 34.

[0024] The structured light source 40 may emit light that operates nearor in the infrared range such that illumination from the structuredlight source is not visible to human vision. The structured light source40 may be configured or programmed to strobe or flash on and off at apredetermined rate such that its activation and deactivation isindependent of control signals issued by the controller 34.

[0025] The structured light source 40 projects light patterns 42 onto anarea of interest 44, in a manner as described below. The light patterns42 may take any form, but preferably are either horizontal or verticalpatterns that appear as stripes in the area of interest 44, or circulardots or spots of light. In the illustrated embodiment, the area ofinterest 44 is on the vehicle occupant 20 on the seat 18. At least onecharacteristic of the light pattern 42, as reflected from the area ofinterest 46, is measured or calculated to provide information useful incontrolling the inflator 28 of the occupant protection system 12.

[0026] The structured light source 40 projects its light patterns 42through a lens 50. The lens 50 is a non-linear lens—that is, either aconverging lens or a diverging lens. In the example shown in FIGS. 1 and2, the lens 50 is a diverging lens. The diverging lens 50 spreads thelight pattern 42 to increase its width at any location past (to the leftas viewed in FIGS. 1 and 2) the lens. As a result, the light pattern 42,exiting from the lens 50, has a width that corresponds to the width of alight pattern that would emanate from a structured light source fartheraway from the occupant than it actually its. Thus, the lens 50 helps tocreate an apparent (virtual) structured light source 52 that is fartherfrom the area of interest 44 than the actual structured light source 40.This is described below in detail.

[0027] The structure for obtaining sensory information regarding thepresence and/or position of an occupant also includes a diffuse lightsource 58 located within the interior of the vehicle 10. The diffuselight source 58 is operatively connected to the controller 34 andselectively illuminates the interior of the vehicle 10 with diffuselight, as described below, in response to a control signal provided bythe controller 34.

[0028] An image sensor 60 is located within the interior of the vehicle10, and is operatively connected to the controller 34. The image sensor60 may be any type of sensor suitable for acquiring an image of theinterior of the vehicle 10. For instance, the image sensor 60 may takethe form of a CCD (charge coupled device) image sensor or camera. Animage captured by the camera 60 is two-dimensional and is providedwithin the camera by an array of pixels. The array may, for example, be640 pixels wide (x-axis image data) and 480 lines or pixels tall (y-axisimage data). Other examples for the camera 60 include a CMOS-typedevice. The camera 60 is preferably located on the same vertical axis (Yaxis) as the structured light source 40, to ensure that the projectedlight pattern 42 stays in the field of view of the camera.

[0029] The image sensor 60 conveys a signal indicative of the acquiredimage to the controller 34. In one embodiment, the image sensor 60 iscontrolled to acquire the images of the interior of the vehicle 10 inresponse to control signals issued by the controller 34. Alternatively,the image sensor 60 may be programmed or configured to acquireautomatically the images of the interior of the vehicle 10 at one ormore predetermined frequencies. In this case, control signals issued bythe controller 34 would be unnecessary.

[0030] To determine the presence and position of an occupant (e.g., theoccupant 20) of the vehicle seat 18, the image sensor 60 initiallyacquires a first image of the interior while only the diffuse lightsource 50 is turned on. The interior of the vehicle 10 is illuminated bydiffuse light to obtain a standard two-dimensional (2-D) image of thearea of interest 44. This image is then sent to the controller 34 forprocessing by conventional 2-D image analysis techniques to determinefeatures of interest within the field of the picture. A number of thesetechniques are known to the art.

[0031] The image sensor 60 then acquires a second image of the interiorof the vehicle 10, when the structured light source 40 is turned on.During this time period, the structured light source 40 projectsstructured light patterns 42 onto the identified area of interest 44. Toensure that the imaged features (i.e., occupant features) have notshifted in the field of view of the camera 60 between sequential imageacquisitions, it is preferred that the first and second images beacquired in rapid succession.

[0032] An example of a determination of an object or occupant's positionfrom analysis of the second image is shown pictorially in FIG. 2. Thelight source 40 projects the light pattern 42 onto the area of interest44 through the diverging lens 50. The width of the light pattern 42increases as the light pattern diverges initially from the light source40. The amount of divergence is increased by the lens 50 to an actualangle of divergence θ_(act). As a result, the pattern of light 42, whenit impinges on the area of interest 44, is wider than it would have beenhad it not passed through the lens 50. The pattern of light 42 thusappears to emanate from an apparent source 52 that lies behind thestructured light source 40 (the actual source)—that is, farther from theoccupant 20 than the actual source 40.

[0033] Because the light pattern 42 is diverging, the actual width ofthe pattern on the area of interest 44 on the occupant 20 isdeterminative of its distance from the apparent source 52. Therelationship can be described mathematically as:

Width=Distance* sin(θ_(app))   (1)

[0034] where θ_(app) is the angle of the apparent source projectionsubsumed by the measured light pattern 42 at the area of interest 44.

[0035] The width of the light pattern 42 on the area of interest 44 isnot measured directly. Instead, the width is determined (calculated)from the size of the angle subsumed by the light pattern as reflected onthe imager 60. For convenience of notation, the distance from the imagesensor 60 and the actual source 40 to the area of interest 44 is labeledB in FIG. 3. The distance from the apparent source 52 to the actualsource 40 is labeled A in FIG. 3. The relationship between the anglesubsumed by the pattern on the image sensor 60 and the width of thelight pattern 42 at the area of interest 44, can be expressed asfollows:

θ_(cam)=sin⁻¹(Width/B)   (2)

[0036] where θ_(cam) is the angle subsumed by the light pattern on thearea of interest.

[0037] Substituting the width value from (1) into (2) and inserting thenew notation of A and B for the relative distances, the relationshipbetween B and the subsumed angle on the image sensor 60 becomes:

θ_(cam)=sin⁻¹[(A+B)* sin(θ_(app))/B]  (3)

[0038] The desirability of using a non-linear lens 50 to distort thelight pattern is apparent from (3). Specifically, if the apparent source52 were in the same front-to-back location as the image sensor 60, forexample as the actual source 40 is in FIG. 1, A would be equal to zero.As a result, B would drop out of the equation, and the subsumed imagesensor angle would become equal to the projection angle for alldistances. Accordingly, all information as to the distance of the areaof interest 44 from the image sensor 60, would be lost. That is, thevalue of θ_(cam) would provide no useful information about the distanceB.

[0039] Assuming a non-zero value for A, however, such as results fromthe use of a non-linear lens 50, B does not drop out of the equation,and there is a unique value of θ_(cam) for each value B. Therefore, itis possible to determine a distance B for a given pattern width. Since Aand θ_(app) are known quantities from the characteristics of the lens 50and the projected light pattern 42, and since θ_(cam) is easilymeasured, B can be calculated as follows:

B=A* sin(θ_(app))/[ sin(θ_(cam))−sin(θ_(app))]  (4)

[0040] This calculation is relatively simple and requires a minimum ofprocessing power. As a result, the distance B to the area of interest44, can be easily calculated on the basis of the width of the lightpattern 42 as it impinges on the area of interest, as viewed by theimager 60.

[0041] An additional benefit of this occupant location system 12 is thatit is unnecessary to place the light sources 40 and 58 in a locationseparate (in the front-to-back direction) from the image sensor 60.Instead, one or both of the light sources 40 and 58 can be packagedtogether with the image sensor 60. This eliminates the costs inherent indual packaging.

[0042] Once the distance of the points on the area of interest 44 fromthe image sensor 60 is determined, the system 12 analyzes their positionin the field of view of the image sensor using conventional 2-Dtechniques. The lateral and vertical position of any point relative tothe image sensor 60 can be determined by processes known in the art, forexample, by noting the angular position of the object within the fieldof view of the camera. Combining this information with the distanceinformation obtained from the calculation discussed above, it ispossible to obtain a true 3-D position for each point. Combining thisinformation with the conventional 2-D image analysis used on the firstimage, it becomes possible to locate and identify objects or occupantsin the interior of the vehicle 10.

[0043] In a second embodiment of the invention, multiple light patternsare projected onto an area of interest. FIG. 3 is an illustration ofsuch a projection. In FIG. 3, the projected light patterns are stripes62 and 70.

[0044] The stripes 62 and 70 are projected onto the area of interest 44using a non-linear lens, as described above with reference to FIGS. 1and 2. Thus, apparent stripe width and location on the area of interest44 can be used as a determinant of distance from the imager.

[0045] Specifically, the first stripe 62 has a midpoint 64, and upperand lower edges 66 and 68. The second stripe 70 is spaced apart from thefirst stripe 62. The second stripe 70 has a midpoint 72, and upper andlower edges 74 and 76.

[0046] The imager 60 determines the upper and lower edges 66 and 68 ofthe first stripe 62. Averaging techniques are then used to determine themidpoint 64 of the first stripe 62. The imager 60 determines the upperand lower edges 74 and 76 of the second stripe 70, and averagingtechniques are used to determine the midpoint 72 of the second stripe70.

[0047] The system 10 considers the spacing between the midpoints 64 and72 of the stripes 60 and 72, respectively, to compute the distance tothe area of interest 44. The distance calculation is similar to thatdiscussed above with respect to a single light pattern 42.

[0048] In a third embodiment of the invention, light patterns (beams) ofa specific, unvarying height are projected onto the areas of interest.The light patterns do not diverge as they extend away from the lightsource. As a result, the apparent height of the light pattern on thearea of interest (that is, how much of the field of view of the camerais taken up by the light pattern), is directly indicative of thedistance between the light source and the area of interest.

[0049]FIGS. 4 and 5 illustrate an occupant location system 12 a inaccordance with the third embodiment of the invention. The parts of thesystem 12 a are the same as those of the system 12 of the firstembodiment, with the exception that the lens 50 is replaced with a beamconverging device 80. Parts that are the same are given the samereference numerals with the suffix “a” attached.

[0050] The beam converging device 80 may be a converging lens, or acollimator, for example. The beam converging device 80 substantiallyeliminates the diverging characteristic of the light beam 42 a. Thus,the light beam 42 a after it leaves the beam converging device 80 is notdiffuse light, but is instead one type of “structured”light-specifically, a narrow beam that does not diverge or convergesignificantly as it approaches the vehicle seat.

[0051] For example, if the beam of light 42 a produced by the lightsource 40 a is round, as shown in FIGS. 4 and 5, then it has asubstantially constant diameter over the distance between the convergingdevice 80 and the seat 18 a. That is, the width (diameter) of the beamof light 42 a does not change significantly over a range between theconverging device 80 and the vehicle seat 18 a even when the seat is asfar back as possible.

[0052] Thus, the actual size of the area of light impinging on anoccupant of the seat 18 a does not change significantly over a range ofobject positions between (a) the vehicle seatback when the seat is asfar back as possible, and (b) an object, such as a person, locateddirectly in front of the converging device 80 (for example, a person onthe floor between the seat and the instrument panel 16). In oneembodiment, the actual diameter size of the light beam 42 a is one totwo centimeters. The light pattern size may, thus, be exaggerated in thedrawings.

[0053] Alternatively, the light source 40 a may, itself, be of the typethat produces a non-diverging light beam. In addition, the light source40 a may project stripes of light, as in FIGS. 1-3, or a type ofstructured light pattern other than a round pattern.

[0054] The light pattern 42 a on the area of interest 44 a subtends anangle at the camera 60 a, and occupies a portion of the field of view ofthe camera. The camera 60 a is operative to generate data representativeof the amount of the field of view of the camera that is occupied by thearea of light 42 a on the illuminated occupant 20 a. As described below,the amount of the field of view that is occupied by the area of light 42a, and the subtended angle, are used to calculate the distance betweenthe instrument panel 16 a and the occupant 20 a, without directmeasurement of that distance. Thus, the camera 60 a is operative togenerate data representative of the distance between the instrumentpanel 16 a and the object (occupant 20 a) on the vehicle seat 18 a.

[0055]FIG. 4 illustrates the area of interest 44 as being on an occupant20 located relatively far from the instrument panel 16 a. FIG. 5illustrates the occupant 20 a as being relatively close to theinstrument panel 16 a. The light pattern 42 a from the light source 40 aimpinges on the occupant 20 a and forms an area of light 82 on thesurface of the occupant. The area of light 82 has a certain size,including a certain height and width.

[0056] Because the light beam 42 a does not diverge over the distancebetween the instrument panel 16 a and the occupant 20 a, the actual sizeof the area of light 82 is essentially constant, no matter where theoccupant is located in this range. The actual size of the area of light82 is a constant.

[0057] As the occupant 20 a gets closer to the camera 60 a, the apparentsize of the area of light 82 increases. The apparent size of the area oflight 22 varies directly with distance.

[0058] The area of light 82 appears in the field of view of the camera60 a, and occupies a certain amount of the field of view of thecamera—in other words, the area of light subtends a certain angleθ_(cam) at the camera. The subtended angle θ_(cam) varies directly withthe apparent size of the area of light 82.

[0059] As a result, the subtended angle θ_(cam) at the camera 60, thatis, the amount of field of view occupied by the area of light 82, variesdirectly with and is linearly and inversely proportional to the distancebetween the light source 40 a and the object 20 a. The subtended angleθ_(cam) thus varies directly with distance.

[0060] Therefore, the controller 34 can rely solely on the subtendedangle θ_(cam) at the camera 60 a, that is, the amount of field of viewoccupied by the area of light 82, in making the object distancedetermination.

[0061] The camera 60 a generates data representative of the amount ofthe field of view of the camera that is occupied by the area of light 82on the illuminated object 20 a, and representative of the angle θ_(cam)subtended by the area of light. The data generated by the imager 60 aare output to the controller 34 a. The controller 34 a includes a memory84 in which are stored values corresponding to certain object distances.The controller 34 includes a comparator 86 that is operative to comparethe output from the imager 60 a with the stored values in the memory 84.The controller 34 a makes a determination as to the distance between theobject 20 a and the instrument panel 16 a.

[0062]FIGS. 6 and 7 illustrate an occupant location system 12 b inaccordance with a fourth embodiment of the invention. The system 12 b issimilar to the system 12 a (FIGS. 4 and 5) in that both use anon-diverging light beam that makes a spot of light on an occupant, in adistance measurement system. In the system 12 b, however, the verticallocation of the spot of light is used as an indirect determinant ofdistance, rather than the size of the spot of light.

[0063] Specifically, the structured light source 40 b is mounted so thatthe light beam 42 b extends at an angle to the horizontal, that is,vertically up or down rather than horizontally. As a result, the centerof the light beam 42 b is at different vertical locations relative tothe imager 60 b, when measured at different distances from the lightsource 40 b.

[0064] For example, in the illustrated embodiment, the light beam 42 bextends upward from the light source 40 b to the occupant 20 b. When thespot of light 82 b is farther away from the light source 40 b, thecenter 83 of the spot of light is relatively high. When the spot oflight 82 b is closer to the light source 40 b, the center 83 of the spotof light is relatively low.

[0065]FIG. 6 illustrates the illuminated object as being an occupant 20b located relatively far from the instrument panel 16 b. The beam oflight 42 b from the illuminator 40 b impinges on the person and forms anarea or spot of light 82 b having a center 83. The spot of light 82 bappears in the field of view of the camera 60 b. The camera 60 bgenerates data representative of the vertical location of the center 83of the spot of light 82 b on the illuminated object 20 b. The datagenerated by the camera 60 b are output to the controller 34 b.

[0066]FIG. 7 illustrates the person 20 b as being relatively close tothe instrument panel 166. The beam of light 42 b from the illuminator 40b impinges on the person and forms an area or spot of light 82 b. Thespot of light 82 b has a center 83 that is higher than the location ofthe center in FIG. 6. The camera 60 b generates data representative ofthe vertical location of the center 83 of the spot of light 82 b on theilluminated object 20 b. The data generated by the camera 60 b areoutput to the controller 34 b.

[0067] The controller 34 b includes a memory 84 b in which are storedvalues of the vertical height of the spot center 83. The valuescorresponds to object distances. On the basis of a reading of the storedvalues, the controller 34 b makes a determination as to the distancebetween the object 20 b and the instrument panel 16 b. Because thelocation of the spot center 83 in FIG. 6 is higher than the location ofthe spot center in FIG. 7, the controller 34 b determines that theoccupant 20 b is farther away from the instrument panel in FIG. 6, andcloser in FIG. 7.

[0068] From the above description of the invention, those skilled in theart will perceive improvements, changes and modifications in theinvention. Such improvements, changes and modifications within the skillof the art are intended to be covered by the appended claims.

Having described the invention, we claim:
 1. Apparatus for determiningthe location of a vehicle occupant in a vehicle interior, comprising: alight source for projecting at least one structured light beam onto anarea of interest in the vehicle interior to form a light pattern on thearea of interest; a beam divergence control device for altering theapparent location of said light source with respect to the area ofinterest; an imager for detecting light reflected from the area ofinterest; means for measuring a characteristic of the reflected light;and means for determining the distance between the imager and the areaof interest based on the measured characteristic of the reflected light.2. Apparatus as set forth in claim 1 wherein said means for measuringincludes means for measuring the apparent width of the light pattern onthe area of interest.
 3. Apparatus as set forth in claim 2 wherein saidlight source projects a circular beam of light, and said means formeasuring measures the apparent diameter of the light pattern on thearea of interest.
 4. Apparatus as set forth in claim 2 wherein saidlight source projects a stripe of light, and said means for measuringmeasures the apparent width of the stripe of light on the area ofinterest.
 5. Apparatus as set forth in claim 2 wherein said means formeasuring measures the vertical location of the center of the lightpattern on the area of interest.
 6. Apparatus as set forth in claim 1wherein said light source projects a plurality of structured light beamson the area of interest to form a plurality of light patterns, and saidmeans for measuring measures a distance between said plurality of lightpatterns.
 7. Apparatus as set forth in claim 8 further comprising: meansfor illuminating the vehicle interior with diffuse light; means fordetecting the reflected diffuse light as an image of the vehicleinterior; and means for processing the detected image to determine thelocation of the area of interest within the vehicle interior. 8.Apparatus as set forth in claim 9 wherein said light source projects alight beam that diverges at a first angle, and said beam divergencecontrol device alters the angle of divergence of the light beam. 9.Apparatus as set forth in claim 8 wherein said beam divergence controldevice increases the angle of divergence of the light beam to a secondangle greater than the first angle.
 10. Apparatus as set forth in claim8 wherein said beam divergence control device decreases the angle ofdivergence of the light beam to a second angle less than the firstangle.
 11. Apparatus as set forth in claim 10 wherein said beamdivergence control device decreases the angle of divergence of the lightbeam to approximately zero.
 12. Apparatus as set forth in claim 1wherein said light source creates a light pattern on the area ofinterest whose apparent width changes at a different rate than the rateof change of the distance between the area of interest and the imager,as the area of interest moves closer to the imager.
 13. Apparatus as setforth in claim 1 wherein said means for determining determines theamount of the field of view of said imager that is occupied by lightreflected from the area of interest.
 14. Apparatus as set forth in claim1 wherein said means for determining determines the angle at said imagerthat is subtended by the light reflected from the area of interest. 15.Apparatus as set forth in claim 1 wherein said means for determiningincludes means for comparing data generated by said imager with storeddata representing a relationship between (a) the distance between theobject and the fixed structure, and (b) the angle at said imager that issubtended by the area of light.
 16. Apparatus as set forth in claim 1wherein said means for measuring includes means for generating datarepresentative of the vertical location of the area of light in thefield of view of the imager.
 17. A vehicle occupant location systemcomprising: illumination means for projecting at least one structuredlight pattern onto an area of interest; means for altering the apparentlocation of said illumination means with respect to the area ofinterest; image sensing means, co-located with said illumination means,for detecting light reflected from the area of interest; and acontroller, operatively connected to said image sensing means, fordetermining the distance of points within the area of interest from saidimage sensing means on the basis of at least one perceivedcharacteristic of the at least one light patterns projected by saidillumination means.
 18. A system as set forth in claim 17 wherein saidmeans for altering alters the apparent distance between saidillumination means and the area of interest.
 19. A system as set forthin claim 17 wherein the distance determination made by said controlleris based on the perceived width of the reflected light patterns.
 20. Asystem as set forth in claim 17 wherein said illumination means projectsa plurality of light patterns and the distance determination by saidcontroller is based on the perceived distance between the midlines of apair of light patterns.
 21. A system as set forth in claim 17 whereinsaid means for altering comprises a lens that alters the angle ofdivergence of said at least one structured light pattern.
 22. A systemas set forth in claim 21 wherein said means for altering eliminatesdivergence of said at least one structured light pattern.
 23. A methodof determining the location of a vehicle occupant in the interior of avehicle, said method comprising the steps of: projecting at least onestructured light pattern from a light source onto an area of interest inthe vehicle; altering the apparent location of the light source withrespect to the area of interest; detecting the reflected light patternwith an image sensor; measuring a characteristic of the light pattern onthe area of interest; and calculating the distance of points on the areaof interest from the image sensor on the basis of the measuredcharacteristic.
 24. A method as set forth in claim 23 wherein said stepof measuring a characteristic of the light pattern includes measuringthe width of the light pattern.
 25. A method as set forth in claim 23wherein said projecting step includes projecting a plurality of lightpatterns from the light source on the area of interest, and saidmeasuring step includes measuring the distance between adjacent lightpatterns on the area of interest.
 26. A method as set forth in claim 23wherein said projecting step includes projecting at least onenon-diverging light pattern from the source onto the area of interest,said measuring step includes measuring the width of the light pattern onthe area of interest, and said calculating step includes determining theamount of the field of view of the imager sensor that is occupied by thereflected light pattern.
 27. A method as set forth in claim 23 whereinsaid projecting step includes projecting a circular light pattern andsaid measuring step includes measuring the apparent diameter of thelight pattern on the area of interest.
 28. A method as set forth inclaim 23 wherein said projecting step includes projecting a lightpattern and said measuring step includes measuring the vertical locationof the center of the light pattern on the area of interest.
 29. A methodas set forth in claim 23 wherein said projecting step includes creatinga light pattern on the area of interest whose apparent width changes ata different rate than the rate of change of the distance between thearea of interest and the imager, as the area of interest moves closer tothe imager.
 30. A method as set forth in claim 23 wherein saidcalculating step includes comparing data generated by the imager withstored data representing a relationship between (a) the distance betweenthe object and the fixed structure, and (b) the angle at the imager thatis subtended by the area of light.
 31. A method as set forth in claim 23wherein said measuring step includes the step of generating datarepresentative of the vertical location of the area of light in thefield of view of the imager.